Monday, 5 May 2014

the role of bacteria on strawberry flavour biosynthesis


Methylobacterium is a plant-associated bacterium, popularly called Pink-Pigmented Facultative Methylotrophs (PPFMs) present in the phyllosphere and rhizosphere of most of the crop plants.  The association of Methylobacterium species with plants seems to rely on a symbiotic relationship between the bacterium and host plants.

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Abstract

Strawberry flavor is one of the most popular fruit flavors worldwide, with numerous applications in the food industry. In addition, the biosynthetic origin of the most important strawberry flavor components, such as 2,5-dimethyl-4-hydroxy-2H-furan-3-one (DMHF), is a challenging research area. DMHF's precursor, 2-hydroxy-propanal (or lactaldehyde), is biosynthesized by the endophytic bacterium Methylobacterium extorquens (M. extorquens). In particular, the alcohol dehydrogenase (ADH) enzymes of M. extorquens are involved in the biogenesis of DMHF precursors since they have the capacity to oxidize the strawberry-derived 1,2-propanediol to lactaldehyde. In this study, the expression of the endophytic ADH and the plant DMHF biosynthesis genes was examined in the tissues of raw and ripe strawberry receptacles by in situ hybridization. The presence of endophytic bacteria was studied in the same tissues by probes targeting bacterial 16S ribosomal Ribonucleic Acid (rRNA). Hybridization signals of probes specific for endophytic ADH and plant DMHF biosynthesis genes, as well as bacteria-specific probes, were detected in the same locations. The probes were localized near the plasma membranes or intercellular spaces of cortical and vascular tissues of the receptacle, and intracellularly in the tissues of achenes. By localizing the expression of the endophytic methanol ADH and plant DMHF biosynthesis genes to the same tissues, we have reinforced our original hypothesis that an intimate symbiotic relationship between strawberry and endophytic cells exists and leads to the biosynthesis of DMHF.

Abbreviations

  • A, Adenine;
  • ADH, alcohol dehydrogenase;
  • C, cytosine;
  • DNA, Deoxyribonucleic acid;
  • DMHF, 2,5-dimethyl-4-hydroxy-2H-furan-3-one;
  • DTT, Dithiothreitol;
  • EDTA, Ethylenediaminetetraacetic acid;
  • FaQR, Fragaria × ananassa quinone oxireductase;
  • G, Guanine;
  • M. extorquens, Methylobacterium extorquens;
  • mxaF, methanol dehydrogenase;
  • PCR, polymerase chain reaction;
  • rRNA, ribosomal Ribonucleic Acid;
  • T, Thymine

Keywords

  • alcohol dehydrogenase enzymes;
  • endophyte;
  • in situ hybridization;
  • Methylobacterium extorquens;
  • strawberry flavor.
Corresponding author contact information
Corresponding author. Tel.: +30 210 7274679.

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